Delivering volumetric fluid flow to a meter under test by metering the fluid flow via timed displacement of a piston moving in a cylinder of known cross section has been an accepted method of flowmeter calibration for many years. Edward E. Francisco, Jr. disclosed a system and method for such an apparatus in U.S. Pat. No. 3,403,544 and in U.S. Pat. No. 3,492,856. Francisco, Jr. teaches the use of a plurality of pistons in a single cylinder to save time by sending first one then a second piston and so on through the calibrated cylinder to accomplish a plurality of test runs before having to return the pistons to the starting end of the cylinder. These earlier disclosed devices are unidirectional piston displacement type volumetric flow rate standards. Fluid flow to a meter under test is metered as the piston moves in the cylinder in one direction. A disadvantage of the apparatus disclosed by Francisco that is overcome by the present invention is the requirement that after the metering pistons have completed a metering run down the cylinder, they must be returned fully to the opposite end of the cylinder before an additional metering run can occur. Lost calibrating time occurs while waiting for the metering pistons to make the transit back to their starting positions. The present invention utilizes timed piston displacement in a cylinder of known cross section to meter volumetric fluid flow rate as do these prior art inventions, but differs substantially from them by virtue of metering the fluid flow rate via bi-directional piston movement and the use of a plurality of cylinders, each with a metering piston therein resulting in improved flowmeter calibrations.
J. H. Hoffman et al disclosed a bi-directional piston displacement type flow and other hydraulic parameter test device in U.S. Pat. No. 3,098,382. A plurality of pistons and cylinders comprise the system disclosed by Hoffman et al. One cylinder with a piston functions only as an actuator while the second cylinder with a piston is the test cylinder used to deliver working fluid to a test component. The present invention differs from that disclosed by Hoffman et al in that the plurality of pistons and cylinders of the present invention are all standards or test cylinders as denoted by Hoffman et al, each cylinder having a metering piston and functioning collectively to reduce the connecting volume of piping required to couple a meter under test to the flow being delivered by a bi-directional piston displacement type volumetric flow rate standard. Reduced volume of piping connecting a flowmeter to the metering cylinder, as achieved with the current invention, provides improved uncertainty of delivered fluid flow at a meter under test over what can be achieved with the apparatus of Hoffman et al. Additionally, working fluid is applied to both sides of the piston in the test or metering cylinder of the invention of Hoffman et al. The present invention applies working fluid to only one side of each piston in the plurality of metering cylinders differing substantially from and providing the ability to measure working fluid temperature adjacent to a metering piston which is an additional non-obvious improvement over the invention of Hoffman et al and all other similar prior art.
Georgi disclosed in U.S. Pat. No. 3,756,456 an apparatus and method for metering and delivering a fluid volume comprising a plurality of cylinders with pistons. One cylinder with a piston in the apparatus disclosed by Georgi is a volumetric pump while the second cylinder with a piston is a bi-directional actuator. Moving in one direction as driven by the actuator, the volumetric pumping cylinder pulls a fluid from a reservoir into the volumetric pumping cylinder. Driven in the opposite direction the volumetric pumping cylinder discharges the fluid to an outside receptacle. The apparatus disclosed by Georgi only meters a volume of fluid and does not consider time of delivery of that volume of fluid to determine a fluid flow rate as does the current invention. The plurality of cylinders with pistons disclosed by Georgi each have different function and do not collectively function in a manner suitable for the calibration of fluid flowmeters as does the current invention. Working fluid is handled in only a single cylinder of the apparatus disclosed by Georgi while in the current invention all of the plurality of cylinders with pistons receive and discharge working fluid and bi-directionally meter the flow of that working fluid with the advantages of near continuous delivery to a flowmeter under test and improved uncertainty of fluid flow rate delivered to said flowmeter under test relative to the flow rate delivered by prior art bi-directional piston displacement type flow rate standards.
Fletcher et al disclosed in U.S. Pat. No. 3,817,082 an apparatus for establishing flow of gaseous fluid in a test section which utilizes a plurality of cylinders with pistons. The pistons in the plurality of cylinders of the apparatus disclosed by Fletcher et al are both driven simultaneously in the same direction to produce two separate flows. One flow is a core flow through a test section while the second flow is the flow near the boundary of the flow chamber walls up steam of the test section. Boundary flow is separated from the core flow by a scavenging means connected to the suction side of the smaller of the flow producing cylinders with a piston. The purpose of the scavenging of boundary flow from the total flow is to liberate the core flow from the effects of the lower velocity boundary flow. The plurality of cylinders and pistons in the apparatus disclosed by Fletcher et al do not function in the manner of the plurality of cylinders and pistons of the current invention to bi-directionally establish a single fluid flow rate through a flowmeter under test derived from a single flow rate metered by piston displacement. The plurality of cylinders with pistons of the apparatus disclosed by Fletcher et al produce a desired test section flow only when driven unidirectionally and do so by discharging working fluid from one side of the pistons while receiving working fluid return flow on the opposite side of the pistons. The current invention both receives and discharges a single flow of working fluid on only one side of the metering pistons in the plurality of cylinders and does so with bi-directional movement of the pistons. Additionally, the current invention is usable with both gaseous and liquid fluids.
Francisco, Jr. later disclosed a piston displacement type volumetric flow rate standard in U.S. Pat. No. 4,152,922 which consists of a plurality of cylinders with pistons. One piston in a larger cylinder is identified as the measuring piston and the second piston in a smaller cylinder is identified as the retracting piston which is coupled to and utilized to return the measuring piston to the starting position after it has completed a unidirectional measuring run to the opposite end of the measuring cylinder. A disadvantage of the apparatus disclosed by Francisco that is overcome by the present invention is the requirement that after the metering piston has completed a metering run down the cylinder, the piston must be returned fully to the opposite end of the cylinder before an additional metering run can occur. Lost calibrating time occurs while waiting for the metering piston to make the transit back to the starting position. The plurality of pistons and cylinders disclosed in U.S. Pat. No. 4,152,922 differ substantially in function and purpose from the plurality of pistons and cylinders disclosed in the present invention in that the plurality of pistons and cylinders of the present invention meter fluid flow bi-directionally and all are utilized for metering of fluid flow.
Jackson disclosed an apparatus for calibrating flowmeters in U.S. Pat. No. 4,307,601. The apparatus disclosed by Jackson utilizes a piston in a cylinder to meter fluid flow coupled by a cable over a pulley to a counterweight situated in a second cylinder. The plurality of cylinders in the apparatus disclosed by Jackson each have different functions. One cylinder with a metering piston serves to measure the fluid flow entering that cylinder while the second cylinder simply protects a counterweight serving to offset the force of gravity acting on the metering piston in the other cylinder and reduce pressurization of the fluid lifting the metering piston. Actual working fluid does not flow into or out of the second cylinder housing the counterweight. The apparatus disclosed by Jackson can only work properly with the cylinders in or very near the vertical position which facilitates the counterweight offsetting the force of gravity on the metering piston. The apparatus disclosed by Jackson does not provide the fluid flow motivation means. The apparatus disclosed by Jackson is limited in use for only gaseous fluid flow. The apparatus disclosed by Jackson does not provide the benefits gained by the use of a plurality of cylinders each with a metering piston therein as provided by the current invention.
Mathieu discloses in U.S. Pat. No. 4,507,952 a bi-directional piston displacement type volumetric flow rate standard with a jacket over the cylinder to provide a passage through which a flow of working fluid around the metering cylinder takes place during operation to equalize the temperature of the metering cylinder with the working fluid. This process additionally provides near equal pressure on both sides of the metering cylinder wall which reduces the effect of working fluid pressure on the metering cylinder cross sectional area. Mathieu also discloses a pressurization means to the downstream side of a meter under test to avoid vaporization of the working fluid during flowmeter calibrations when the working fluid is liquid. Preferred embodiments of the present invention incorporate these teachings of Mathieu. Temperature equalization, control of liquid fluid pressure above the vapor point throughout the flow circuit and pressure equalization on both sides of the metering cylinder wall are best practices in the art. The present invention represents an improvement in the accuracy of delivered flow rate to a meter under test over what can be accomplished in the disclosed invention of Mathieu. The improvement is achieved by quantifying and accounting for the thermal effects to fluid density passing through the connecting volume between the metering piston and meter under test during standard volume delivery and by significantly reducing the connecting volume to standard volume ratio by both operational method and physical reduction of the required connecting volume piping for a bi-directional piston displacement type volumetric flow rate standard as well as by providing temperature measurement of the working fluid adjacent to the metering pistons. Connecting volume is defined as the sum of fluid volume in piping connecting the metering cylinder outlet with the inlet to the flowmeter under test and the residual volume of fluid in the cylinder between the cylinder outlet and the metering piston at the end of standard volume delivery. Standard volume is defined as the volume of fluid delivered from the calibration apparatus to a flowmeter under test during the collection of a single data point from the flowmeter under test.
Cohrs et al disclose a piston displacement type volumetric fluid flow rate standard in U.S. Pat. No. 4,627,267 which incorporates a plurality of pistons and cylinders in the process. As in both U.S. Pat. No. 3,098,382 and U.S. Pat. No. 4,152,922 the plurality of pistons and cylinders comprise first a single measuring cylinder and secondly what is referred to as an actuating cylinder, retracting piston or control piston. A disadvantage of the apparatus disclosed by Cohrs et al that is overcome by the present invention is the requirement that after the metering piston has completed a metering run down the cylinder, the piston must be returned fully to the opposite end of the cylinder before an additional metering run can occur. Lost calibrating time occurs while waiting for the metering piston to make the transit back to the starting position. The present invention incorporates a plurality of pistons and cylinders each of which functions bi-directionally as a metering device and which work collectively to reduce the connecting volume between the metering piston and the meter under test. The plurality of pistons and cylinders disclosed in the present invention function substantially different from and with the advantage of faster and higher accuracy flowmeter calibration relative to the plurality of pistons and cylinders disclosed by Cohrs et al in U.S. Pat. No. 4,627,267 and other similar prior art.
U.S. Pat. No. 4,627,267 further discloses a metering piston displacement measurement process incorporating a shaft attached to and moving with the metering piston and carrying an optical encoder head which moves relative to an inscribed linear ruler surface to produce a pulsed electrical signal with the number of pulses representing directly the linear axial displacement of the metering piston. Preferred embodiments of the present invention incorporate the use of such an optical encoder as the means to accurately measure the metering piston displacement during flowmeter calibration operations. Also disclosed in U.S. Pat. No. 4,627,267 is a position sensor. This position sensor relates to the position of a seal leak detection device and is substantially different from the position sensor disclosed in the present invention. The position sensor of the present invention is utilized to determine the position of the metering piston relative to the discharge end of the cylinder in which it is traveling for the purpose of positioning the metering piston to a proper starting position, traversing the metering piston to the discharge end of the cylinder during delivery of a standard volume and determining the fluid volume in the cylinder between the piston and cylinder discharge (dead volume) at the end of a standard volume delivery. These functions in the current invention collectively contributing to the improved uncertainty of fluid flow rate delivered to a flowmeter under test relative to the uncertainty of flow rate delivered to a flowmeter under test by prior art bi-directional piston displacement type flow rate standards while reducing the time to calibrate flowmeters under test.
Cohrs et al later disclosed in U.S. Pat. No. 4,674,317 an apparatus for determining the flow characteristic of a volumetric flowmeter which utilizes a plurality of cylinders with pistons. One cylinder with a piston therein is utilized to unidirectionally meter the flow of working fluid. A second cylinder with a piston therein is a control divice coupled to and used to drive the metering piston in the first cylinder. The plurality of cylinders with pistons in the apparatus disclosed by Cohrs et al do not function to facilitate bi-directional metering of working fluid flow and do not function to improve the uncertainty of flow rate delivered to a flowmeter under test by reducing connecting volume requirement as do the plurality of cylinders with pistons of the current invention. A disadvantage of the apparatus disclosed by Cohrs et al that is overcome by the present invention is the requirement that after the metering piston has completed a metering run down the cylinder, the piston must be returned fully to the opposite end of the cylinder before an additional metering run can occur. Lost calibrating time occurs while waiting for the metering piston to make the transit back to the starting position.
West disclosed in U.S. Pat. No. 4,829,808 a flowmeter prover apparatus and method which utilizes a plurality of cylinders with pistons. Flowmeter provers are not laboratory standards, but are field standards employed for in place proving of the accuracy of an installed flowmeter. In the apparatus disclosed by West, one cylinder with a piston therein is utilized to unidirectionally meter fluid flow after being plumbed in series with a flowmeter under test. A second cylinder with piston is coupled to the metering piston and serves to dampen the acceleration and movement of the metering piston through the metering cylinder. Working fluid does not flow into or out of the second cylinder with piston therein and does not serve to meter fluid flow. A third cylinder with a piston therein is utilized to supply a fluid under pressure into a space between seals on the metering piston. This third cylinder with a piston therein is not utilized to meter working fluid flow, but is a means for improving the function of the seals on the single metering piston. Working fluid does not flow into or out of the third cylinder with piston of the apparatus disclosed by West. The plurality of cylinders with pistons therein of the apparatus disclosed by West do not function to facilitate bi-directional metering of working fluid and do not function to reduce the required connecting volume between a metering piston and a flowmeter under test as do the plurality of cylinders with pistons of the current invention.
Halpin discloses in U.S. Pat. No. 4,854,154 and again in U.S. Pat. No. 5,111,682 a piston displacement type volumetric fluid flow rate standard for flowmeter calibration. The systems disclosed by Halpin are for unidirectional piston displacement operation and differ substantially from the present invention. A disadvantage of the apparatus disclosed by Halpin that is overcome by the present invention is the requirement that after the metering piston ha's completed a metering run down the cylinder, the piston must be returned fully to the opposite end of the cylinder before an additional metering run can occur. Lost calibrating time occurs while waiting for the metering piston to make the transit back to the starting position. The current invention facilitates bi-directional metering of fluid flow by the pistons slidably mounted in the plurality of cylinders and further employs a method of controlling the end point and starting point of metering pistons during standard volume delivery to both produce a standard volume of sufficient quantity to assure meeting a predetermined level of flow rate uncertainty while minimizing that required quantity with the ending point being at a position in the metering cylinder nearest to the cylinder discharge. The conduit piping volume between the metering cylinder discharge and the flowmeter under test is also minimized in the current invention to further reduce the required standard volume quantity necessary to meet a predetermined uncertainty of flow rate at the flowmeter test and thus reduce to time to deliver that standard volume quantity.
Halpin does disclose in U.S. Pat. No. 4,854,154 the use of a reservoir means with pressurized gas over liquid fluid therein to maintain a near constant fluid pressure. This being similar to the pressurization means disclosed by Mathieu in U.S. Pat. No. 4,507,952 to prevent liquid fluid pressure from falling below vapor pressure. Preferred embodiments of the present invention include the pressurized reservoir means to prevent vaporization of liquid working fluid at any location in the process and in particular the prevention of liquid fluid vaporization at the trailing edges of turbine flowmeter blades when such flowmeters are meters under test. Avoiding fluid vaporization when the working fluid is a liquid is required for proper calibration operation. The teachings of Mathieu and Halpin regarding the use of a reservoir with gas over liquid pressurization to prevent working fluid vaporization are best practices in the art.